1. Field of the Invention
The invention relates to the field of nutrition and food sciences. In particular, the invention relates to soy meat compositions with improved organoleptic properties such as decreased odor and methods for the use and production thereof.
2. Description of Related Art
Soybeans provide high quality proteins that provide health benefits for humans (Hermansen et al., 2003; Bazzano et al., 2001; Food and Drug Administration, 1999). The demand for soybeans to make soy foods had not gone up as much as expected in last three decades (Wolfe and Cowan, 1975 and SoySource, The United Soybean Board 1999). This is in-part because of the undesirable odor associated with soy products (McLeod and Ames, 1988 and Freese, 1999). The undesirable soybean odor is commonly described as “beany.” Components that impart beany characteristic to soybeans include many volatile fatty acids, aliphatic carbonyls, amines, alcohols, aldehydes, and furans derived from the action of enzymes on various compounds found in soybeans and their further oxidation that is caused by many mechanisms (Wolfe and Cowan, 1975; Sessa and Rackis, 1977).
Kobayashi et al. (1995) concluded the main contributors to the odor of uncooked soymilk were (trans, trans)-2,4-nonadienal, (trans, trans)-2,4-decadienal, hexanal, 2-pentyl furan, 1-octen-3-one, (trans)-2-nonenal, and (trans, cis)-2,4-nonadienal. The strongest odors extracted from heat-treated soymilk were identified as (trans, trans)-2,4 decadienal and n-hexanal (Feng, Cornell University Ph.D. Dissertation, 2000). The formation of (trans, trans)-2,4 decadienal take place at a slow rate at room temperature (Frankel, 1988), however this reaction is enhanced because of thermal degradation during soybean processing under hot conditions (Lin, 2003). Other contributors to odors were (trans)-4,5-epoxy-(E)-2-decenal (formed from 2,4 decadienal), (trans, cis)-2,6-nonadienal, (trans)-2-nonenal, (trans, trans)-2,4-nonadienal, 2,4 nonadienal, maltol, vanillin and β-damascenone. The most powerful odorants in soymilk determined by the minimum headspace volume required to detect by olfactometry, were hexanal, acetaldehyde, methanethiol, dimethyl trisulfide, and 2-pentyl furan (Boatright, 2002).
The strongest odorants in soy protein isolates were identified as dimethyl trisulfide, (trans, trans)-2,4-decadienal, 2-pentyl pyridine, (trans, trans)-2,4,-nonadienal, hexanal, acetophenone, and 1-octen-3-one (Boatright and Lei, 1999). The mechanism of formation of methanethiol and dimethyl trisulfide involves free radicals formed by lipid oxidation (Lei and Boatright, 2003) and products of enzymes such as cysteine synthase (Boatright, 2003, poster 45C-26, IFT annual meeting, Chicago).
The formation of 2-pentyl pyridine occurs from a spontaneous reaction between 2,4 decadienal and ammonia at room temperature. Free amino acids arginine, lysine, asparagine and glutamine increase 2-pentyl pyridine formation probably by providing ammonia during soy protein processing. (Zhou and Boatright, 2000; Kim et al., 1996). Free amino acids can also form other undesirable products. High temperature exposure of asparagine and glucose results in the formation of acrylamide (Jung et al., 2003). Arginine exposed at cooking temperatures can form mutagens (Knize et al., 1994). Free arginine was enriched in soybeans lacking both β-conglycinins and glycinins (Takahashi et al., 2003).
Once formed, odors are difficult to remove from soy ingredients because they are associated with proteins (Franzen and Kinsella, 1974). The quality of natural flavors added to soy foods are also altered unfavorably because some of the odors bind to soy protein. Carbonyl compounds and 2-pentyl pyridine bound with greater affinity to glycinin fractions than β-conglycinin fractions (Zhou et al., 2002; O'Keefe et al., 1991). The extraction of oil-body-associated proteins and polar lipids significantly reduced the quantity of odors associated with soy protein isolate (Samoto et al., 1998).
Textures created by protein-protein interactions can have more effect on flavor intensity than the in-nose odor concentration (Weel et al., 2002). Soy proteins can contribute to the poor organoleptic quality of soy beverages by forming insoluble aggregates and chalky mouthfeel (Skarra and Miller, 2002). Among the main soy proteins, glycinins are more sensitive to pH and Ca+2-induced insolubilization (Yuan, 2002) and soybeans containing a low ratio of glycinins to β-conglycinins are useful for creating soluble soy protein ingredients (U.S. Pat. No. 6,171,640). Lipid oxidation reactions also influence protein solubility. Antioxidants can be added during soy protein isolate manufacture to limit free radical induced oxidation of proteins and improve the yield of soluble protein (U.S. Pat. No. 5,777,080). Some peptides can react during processing with polysaccharides to form antioxidant compounds (Matsumura, 2003).
Color influences perceptions of freshness and taste (Joshi, 2000). Low amounts of reducing sugar and aldehydes formed from lipid oxidation react with amino groups of proteins on heating to form brown pigments by the Maillard's browning reaction (Kwok et al., 1999). Soymilk with a higher content of aldehydes will create a darker, less appealing color after heat processing. On the other hand lipid oxidation during soymilk processing decolorizes yellow pigments in soymilk (Obata and Matsuura, 1997).
Soybeans are refined to improve the flavor by extracting lipids and other components either by alcohol extraction, enzyme treatments, washing protein curds, ultrafiltration of protein and or use of flash vaporization. These processes add to the cost of the soy protein ingredients and typically lower the amounts of healthful components that are bioavailable (for example fiber, oligosaccharides, isoflavones, polyunsaturated fatty acids, tocopherols, phospholipids, bioactive peptides). Processing approaches used to improve the organoleptic properties of soy protein ingredients are limited in effectiveness by odors bound to soy proteins and by conditions that promote odor formation (pH 8-10). Soybeans that lack one to three of the lipoxygenases 1, 2, and 3 were created using mutation breeding to reduce the formation of beany odors (Hajika et al., 1991). Aroma analysis of soymilk and soy flour made from soybeans lacking the three lipoxygenases were found to contain lower amounts of several odors, but higher amounts of 1-octen-3-ol than the parent soybean line containing all three lipoxygenases (Hao et al., 2002). Similar levels of 2,4 decadienal were found in defatted flour and soy protein isolate made from one soybean lacking three lipoxygenases and two other soybean lines (Boatright et al., 1998). Soy foods prepared from soybeans lacking lipoxygenases had improved flavor compared to foods made from control soybeans (Wilson, 1996). Soymilk prepared from soybeans lacking three lipoxygenases was perceived as more bitter than the control, especially after 15 months of seed storage, but this difference was expected to be eliminated by adding sugar (Torres-Penaranda and Reitmeirer, 2001).
Transgenic modifications are proposed to improve the flavor of soybeans by reducing the levels of polyunsaturated fatty acids (U.S. Pat. No. 5,981,781), lipoxygenases (U.S. Patent Appln. 20030074693) and or hydroperoxide lyases (U.S. Pat. No. 6,444,874). Soybeans containing less than 10% polyunsaturated fatty acids and greater than 75% oleic fatty acids yield frying oil that is less tasty compared to frying oil with higher polyunsaturated fatty acids (Warner et al., 2001).
Chemicals such as polyphosphates (U.S. Pat. No. 6,355,296) can be used to limit off-favor production and improve protein solubility. Other additives such as gallic acid (PCT WO 01/06866) or aldehyde oxidase (Maheshwari et al., 1997) can be used to remove odors.
There is little published information on the effects of natural genetic variations on flavor and color attributes of soybeans. The thiobarbituric acid number for 16 soybean varieties was determined as a measure of lipid oxidation and no correlation was found with the vitamin E content of the soybeans (Dahuja and Madaan, 2004). The amounts of 2-pentyl pyridine and 2,4 decadienal in soy flour and soy protein isolate made from three soybean varieties were determined (Zhou and Boatright, 1999). The effects of drying conditions on the removal of the green pigment, chlorophyll from soybeans were studied (Salete et al., 2003; Sinnecker et al, 2002).
In past decades scientists showed that oils prepared from soybeans lacking lipoxygenases did not have improved oxidative stability. Soybean proteins produced from lipoxygenase null soybeans still contained significant levels of beany taste (Maheshwari et al., 1997).
The first step in making soymilk or soy protein ingredients is to dehull (or decoat) the soybeans to create soybean meats. Hypocotyls may also be separated from the cotyledons. Soybean meats are defined as dehulled soybeans and may or may not include cotyledons. A method for preparing meats is described, for example, in U.S. Pat. No. 5,727,689. One method for dehulling includes, but is not limited to, running seeds between counter-current rollers or a cracking mill and aspirating light weight hulls, leaving the meats. Meats may be soaked in water to produce soymilk or flaked and extracted using hexane as an initial step in making defatted soy flour, soy protein concentrates, soy protein isolates and purified protein fractions, as desired.
The present invention provides a new method to determine the ability of soybean meats to resist production of key odor compounds identified as 2,4 decadienal, hexanal, hexanol and 1-octen-3-ol. These compounds were selected as indicators of the extent of different types of oxidation reactions. Hexanal and hexanol result from the breakdown of hydroperoxide containing compounds (peroxides on 9 and 12 carbon positions of fatty acids) by hydroperoxide lyases and alcohol dehydrogenases. 2,4 decadienal is a breakdown product of the lipoxygenase pathway which is not known to involve hydroperoxide lyases. 1-octen-3-ol is formed by the action of hydroperoxide lyases on hydroperoxides formed on the 10 carbon position of linoleic acid. These compounds can react further by additional processing to form more potent odors. For example, 2,4 decadienal is involved in the formation of 2-pentyl pyridine and 1-octen-3-ol is involved in the formation of 1-octen-3-one.